CN108326425B

CN108326425B - Focal plane rotation laser spot welding method

Info

Publication number: CN108326425B
Application number: CN201810231592.6A
Authority: CN
Inventors: 肖荣诗; 彭书胜; 武强
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2018-03-20
Filing date: 2018-03-20
Publication date: 2021-01-01
Anticipated expiration: 2038-03-20
Also published as: CN108326425A

Abstract

A focal plane rotation laser spot welding method is suitable for laser spot welding of metal materials. Is characterized in that the laser spot does small-radius, high-frequency and uniform-speed circular motion on the surface of the workpiece. During welding, the focal point rotating frequency is 10-120 HZ; the focal point rotating radius is 1.0-2.5 mm; the laser power is 600-3000W; the spot welding time is 0.4-3.0S; the defocusing amount is-3 to +3 mm. The invention has the beneficial effects that: by matching the focus rotation parameter and the welding process parameter, the novel weld morphology based on the thermal conductivity welding in the repeated welding heat accumulation mode is obtained, the width-depth ratio (effective fusion width/fusion depth) is large, and the defects of pores, cracks, beds and the like are avoided. Compared with the traditional laser spot welding, the welding process is stable, the quality of the welding seam is better, the influence of the contact thermal resistance between the overlapping interfaces on the effective fusion width (fusion surface fusion width) can be ignored, the width-depth ratio of the welding seam is greatly increased, and the method has obvious process advantages.

Description

Focal plane rotation laser spot welding method

Technical Field

The invention relates to a focus rotating laser spot welding method capable of obtaining the appearance of a spot welding seam with a large width-depth ratio (effective fusion width w/fusion depth h). The welding method can obtain the spot welding seam with larger width-depth ratio (w/h), changes the appearance of the 'nail head' welding seam with large depth-width ratio of the traditional laser spot welding, has obvious advantages in the spot welding of thin plate members and some special members, and belongs to the technical field of material processing.

Background

In the laser processing field, laser spot welding has numerous advantages compared with resistance spot welding, such as high precision, accurate energy control, good penetrability, small welding thermal deformation and the like, and is gradually used as a substitute technology to be widely applied to the fields of aerospace, automobile and ship manufacturing and the like. As an advanced spot welding mode, the spot welding method has some limitations, particularly for high-power laser spot welding, generally, deep melting mode spot welding, the process is violent, large particle splashing behavior is easy to generate, and defects such as air holes, cracks, tatting and the like are easy to generate at extremely high heating and cooling speeds. The traditional laser spot welding 'nail head' shape welding line appearance is the reason that the penetrability is better, but for the overlap spot welding of some thin-walled components, the existence of the contact thermal resistance between the overlap interfaces enables the downward transmission of the peripheral heat of a deep melting small hole in the spot welding process to be limited, the downward flow of a molten pool is blocked, so that the effective melting width (the melting width of a fusion surface) is limited in the range with small periphery of the deep melting small hole, and finally the welding line appearance is changed into 'T' shape from 'nail head', thereby greatly reducing the mechanical property of welding points. Moreover, for some special complex three-dimensional thin-walled components that require non-penetration welding, excessive penetration will tend to cause the component to weld through. The spot welding method adopting the laser focus rotation has the advantages that the welding process is stable and free of splashing, welding spots have no defects of air holes, cracks, tatting and the like, the quality of the obtained welding spots is superior to that of the traditional laser spot welding, and the welding spots have obvious advantages compared with the traditional laser spot welding in the spot welding of thin-wall components due to the large width-depth ratio (w/h) and the special spot welding appearance.

The method adopts a wedge-shaped mirror to deflect the laser beam, and the wedge-shaped mirror is driven by a horizontal rotating motor to horizontally rotate at a constant speed, so that the laser beam rotates at a constant speed (the rotating method refers to the invention patent entitled to the subject group, namely a laser welding method with focus rotation and vertical vibration, and the patent number is 201510907271X.). The deflected beam rotating at high speed acts on the surface of the workpiece, so that the focus rotates around a point on the surface of the workpiece at high speed with a small radius. Under the continuous action of the laser, the materials are rapidly and repeatedly welded to form a welding spot. The invention is characterized in that high-frequency rotation of a laser focus is utilized to coordinate and control laser energy input, so that the single-time laser welding mechanism is thermal conduction welding, the high-frequency repetitive movement of laser continuously accumulates heat of an action area, the melting behavior of a molten pool is continuously enhanced, and finally, the W-shaped welding seam appearance with good forming is obtained. The effective fusion width is large, and the mechanical property of a welding spot can be greatly improved; and the penetration is small, and the welding penetration can be effectively avoided in the spot welding of some thin-wall components. Meanwhile, the mechanism of the spot welding method is a repeated welding heat accumulation process of thermal conductivity welding, so that the welding process is stable and has no splashing, and the welding spot has no defects of tatting, cracks, air holes and the like. Compared with the traditional laser spot welding, the spot welding method improves the quality of welding spots, and the larger width-depth ratio (w/h) and the special spot welding appearance have obvious advantages in the laser spot welding of thin-wall components.

Disclosure of Invention

The invention aims to provide a focal point rotating laser spot welding method, which can effectively solve the problem that interface thermal resistance limits the effective fusion width of a welding spot in the traditional laser overlap spot welding, greatly improve the width-depth ratio (w/h) of the welding spot, has the defects of stable welding process, no splash, bed falling, cracks and the like, and is suitable for laser spot welding of metal materials.

The focal plane rotating laser spot welding method is characterized in that: the laser focus is controlled by the light beam to do circular reciprocating motion with high frequency, small radius and uniform speed on the surface of the workpiece around one point.

The focal plane rotating laser spot welding method is characterized in that: laser spot welding is based on the repeated welding heat accumulation effect of thermal conductivity welding, makes the single welding be thermal conductivity welding through matching laser power and rotational frequency, and through the high-frequency circular motion of laser action position for the continuous accumulation of action zone heat, the melting action of molten bath constantly strengthens, makes annular molten bath intermediate metal base body melt and form circular molten bath through certain welding time, finally obtains the spot welding seam appearance of big aspect ratio (w/h). For example, the width-to-depth ratio (w/h) is not less than 2.

The focal plane rotating laser spot welding method has the main process parameter levels that the focal spot rotating radius is 1.0-2.5 mm, the focal rotating frequency is 10-120 HZ, the laser power is 600-3000W, the spot welding time is 0.4-3.0 s, and the defocusing amount is-3- +3 mm.

The section figure of the obtained welding line along any rotating diameter direction is W-shaped welding line appearance.

The invention has the following beneficial effects: by matching the focus rotation parameter and the welding process parameter, the novel weld morphology based on the thermal conductivity welding in the repeated welding heat accumulation mode is obtained, the width-depth ratio (w/h) is large, and the defects of pores, cracks, tatami and the like are avoided. Compared with the traditional laser spot welding, the welding process is stable, the quality of the welding seam is better, particularly in the lap spot welding of some thin-wall components, the influence of the thermal contact resistance between the lap interfaces on the effective fusion width can be ignored, the width-depth ratio (w/h) of the welding seam is greatly increased, and the laser spot welding has obvious process advantages.

Drawings

FIG. 1 is a schematic view of a focal spot rotary laser spot weld;

FIG. 2 shows the cross-sectional profile and the width-to-depth ratio (w/h) of the solder joint obtained in example 1;

in fig. 1, a wedge-shaped mirror, 2, a laser beam, 3, a focusing mirror, 4, an upper plate material, 5, a welding spot, 6, a lower plate material, theta is an inclination angle of the wedge-shaped mirror, and is a laser beam deflection angle, f is a focal length of the focusing mirror, r is a focal point rotation radius, w is an effective fusion width (fusion surface fusion width), and h is fusion depth.

Detailed Description

The present invention will be further illustrated with reference to the following examples, but the present invention is not limited to the following examples.

Example 1

The adopted equipment comprises: wedge lens, focusing lens, upper plate material, laser. The laser, the wedge-shaped lens, the focusing lens and the upper plate material are sequentially arranged from top to bottom, the laser emits parallel light beams, the parallel light beams are perpendicular to the upper surface of the wedge-shaped lens and then reach the focusing lens through the inclined lower surface of the wedge-shaped lens, the parallel light beams reach the surface of the upper plate material through focusing and focus offset of the focusing lens, and the wedge-shaped lens is rotated at a constant speed in the welding process, so that the focus does circular motion at a constant speed on the upper plate material.

Example 1 the welding process parameters are shown in the following table:

wherein P is laser power, t is spot welding time, DF is defocusing amount, the specified focus is positive when being positioned on the surface of a workpiece, the F focus rotating frequency and r are the focus rotating radius, the laser used in the embodiment is an IPG-YLS6000 optical fiber laser, the focal length of a focusing mirror is 300mm, the protective gas is Ar gas, and the gas flow is 15L/min; the material used in the embodiment is a GH3128 thin plate, the spot welding mode is lap joint, the thickness of the upper plate is 1mm, the thickness of the lower plate is 3mm, the surface and the lap joint surface of the workpiece are polished to remove an oxide film before welding, and then acetone is used for removing impurities and oil stains.

As can be seen from the cross-sectional morphology and the width-to-depth ratio (shown in FIG. 2) of the welding spot, in the embodiment 1, the cross-sectional morphology of the welding spot obtained under different welding parameters is in a T shape in the conventional laser spot welding mode; the effective fusion width (fusion surface fusion width) is obviously limited by the contact thermal resistance between the lapping interfaces, so that the effective fusion width (fusion surface fusion width) is small, the surface fusion width is large, and the width-depth ratio (w/h) of a welding spot is small under different parameters. Meanwhile, the welding spot has poor quality and has the defects of air holes, beds and the like. The focus rotating laser spot welding can obtain the W-shaped welding spot section morphology by adopting optimized process parameters under different rotating frequencies, thereby fundamentally solving the influence of contact thermal resistance between interfaces, greatly increasing the effective fusion width, and greatly improving the width-depth ratio (W/h) of welding spots. And the welding spot has good quality and has no defects of cracks, pores, beds and the like. The results show that under the conditions of the embodiment, compared with the traditional laser spot welding, the focal point rotation laser spot welding has the advantages of large welding point width-depth ratio (w/h) and higher welding point quality, and particularly has remarkable advantages in laser sheet lap welding.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A thin-wall component focal plane rotation laser spot welding method is characterized in that: laser spot welding is a repeated welding heat accumulation effect based on thermal conductivity welding, single welding is thermal conductivity welding by matching laser power and rotation frequency, heat in an action area is continuously accumulated by high-frequency circular motion of a laser action position, the melting behavior of a molten pool is continuously enhanced, a metal matrix in the middle of the annular molten pool is melted into a circular molten pool after a certain welding time, and finally spot welding seam appearance with large width-depth ratio is obtained; the width-depth ratio is not less than 2;

during welding, the main technological parameters are as follows: the rotating radius of a focus spot is 1.0-2.5 mm, the rotating frequency of the focus is 10-60 HZ, the laser power is 600-3000W, the spot welding time is 0.4-3.0 s, and the defocusing amount is-3 to +3 mm;

the cross section of the obtained welding line along any rotating diameter direction is in a W-shaped welding line shape.